A three-dimensional frequency selective absorber with broadband absorption characteristics

Abstract

The present invention belongs to the technical field of absorbent-transmitter integrated materials, and relates to a frequency selective surface radar absorber (FSR), and specifically provides a three-dimensional frequency selective absorber with broadband absorption characteristics. The present invention consists of a three-dimensional absorption structure at the top and a two-dimensional frequency selective surface (FSS) at the bottom. In the three-dimensional absorption structure, a conductive ink impedance film is used instead of a lumped resistor to absorb the incident electromagnetic wave; at the same time, the bottom is provided with a two-dimensional frequency selective surface structure to achieve a low insertion loss transmission band in the working frequency band; the frequency selective absorber provided by the present invention has an absorption band in the X band and the Ku band, and has both a wide absorption bandwidth and a small insertion loss, and has the advantages of small size, easy and flexible assembly, and good angular stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of absorbent-transmitter integrated materials, relates to a frequency selective surface radar absorber (Frequency Selective Rasorber, FSR), and specifically provides a three-dimensional frequency selective absorber with broadband absorption characteristics. Background Art

[0002] Frequency Selective Surface (FSS) is a periodic structure that can transmit and reflect specific frequencies. In recent years, it has been widely used in communication systems, military stealth, and electromagnetic compatibility. However, traditional radomes, represented by FSS, reflect incident electromagnetic waves to other directions to reduce radar cross-sections. This method is only effective in suppressing the radar cross-section of a single base station, and cannot effectively reduce the radar cross-section of dual or multiple stations. In order to overcome this problem, researchers integrated the bandpass frequency selective surface with a metamaterial absorber and proposed a new metamaterial that has both absorbing function and transmission window. This metamaterial is also called frequency selective surface radar absorber (FSR). From the perspective of practical application, FSR not only does not affect the transmission of the normal working signal of the antenna, but also has a strong absorption effect outside the working frequency band. It has a perfect radar cross-section reduction effect on radars of multiple base stations, and can also reduce the mutual interference between different subsystems that make up a large communication system.

[0003] According to the relative position of the transmission band and the absorption band in the FSR, it can be mainly divided into three types: low-transmittance and high-absorption FSR (TA), low-absorption and high-transmittance FSR (AT), and middle-transmittance and two-side absorption FSR (ATA). In addition, it can be divided into two-dimensional FSR and three-dimensional FSR according to the structural design. After years of development, the design of FSR has been widely used in engineering; however, with the development of engineering applications, higher requirements are put forward for the design of antenna covers, such as: 1) smaller unit size and good angle stability, 2) good frequency selectivity, 3) multi-mode resonance characteristics, and great freedom in regulating the zero / pole of electromagnetic wave transmission. At present, most frequency selective radar absorbers cannot meet the characteristics of good transmittance and wide absorption band at the same time; in addition, most current designs require a large number of lumped resistors to be installed on the PCB model, which increases the manufacturing difficulty and total cost.

[0004] For example, the literature "A Miniaturized Absorbtive Frequency Selective Surface (Chen, Q., et al. (2015)). IEEEAntennas and Wireless Propagation Letters 14: 80-83. "A miniaturized frequency selective surface is disclosed, which transmits waves near 0.92 GHz with an insertion loss of -0.5 dB, absorbs waves at 2.8-9 GHz, and the absorption frequency is more than 90%; but the absorption frequency band is in the S and C bands, and the absorption frequency band is relatively low.

[0005] For example, in the document “Design of miniaturized and ultrathin absorptive / transmissive radome with wideband absorbing property (Yi, B., et al. (2016). Microwave and Optical Technology Letters 58 (8): 1870-1875.”, its absorption frequency band is 5.3-14.8 GHz, and the passband frequency can be adjusted by simply loading different capacitors without affecting the absorption characteristics. However, when adjusted to high frequency, the absorption effect will be poor, and certain grating lobes will appear.

[0006] For example, the document "K. Xue, H. Zhai, S. Li, and Y. Shang, A Miniaturized Absorber Frequency Selective Surface With Good Angular Stability. IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 1, pp. 24-28, 2020." discloses a miniaturized TA-type FSR that combines a 3D impedance absorbing layer and a 2D frequency selective layer. The upper 3D structure is two elliptical metal rings containing resistors, which provide an absorption band of 12 to 18 GHz (relative bandwidth 40%). The bottom is a FSS with a bent cross structure, with a transmission point at 4.5 GHz and a minimum insertion loss of 0.5 dB. The FSR has a relatively narrow absorption bandwidth, a transmission point in a higher frequency band, and a higher insertion loss.

[0007] It can be seen that there are still many problems to be solved in the engineering application of existing frequency selective radar absorbers; specifically: 1) The absorber's absorbing band is only in the Ku band, and there are fewer designs in the X band and Ku band, and the relative bandwidth is narrow; 2) Under the same requirements of the absorbing band, it is impossible to maintain a large absorbing bandwidth and good transmittance; 3) A large number of resistor elements need to be loaded, which is costly; 4) The structure is single and cannot be flexibly assembled. Based on this, the present invention proposes a three-dimensional frequency selective absorber with broadband absorption characteristics. Summary of the invention

[0008] The purpose of the present invention is to provide a three-dimensional frequency selective absorber with broadband absorption characteristics in response to many problems raised by the background technology. The absorber is composed of a three-dimensional absorption structure at the top and a two-dimensional frequency selective surface (FSS) at the bottom. In the three-dimensional absorption structure, an impedance film is used instead of a lumped resistor to absorb the incident electromagnetic wave. At the same time, the bottom is provided with a two-dimensional frequency selective surface structure to achieve low insertion loss wave transmission in the working frequency band. The frequency selective absorber provided by the present invention has an absorption band in the X band and the Ku band, has a wider absorption bandwidth and a smaller insertion loss, and has the advantages of small size, easy and flexible assembly, and good angular stability.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A three-dimensional frequency selective absorber with broadband absorption characteristics, which is composed of a three-dimensional absorption structure and a two-dimensional frequency selective surface (FSS). It is characterized in that the XOY plane is used as a horizontal plane, the two-dimensional frequency selective surface is arranged along the horizontal plane, and the three-dimensional absorption structure is arranged directly above the two-dimensional frequency selective surface, and an air layer is formed between the two.

[0011] The two-dimensional frequency selective surface is in a periodic array structure, and the array unit of the two-dimensional frequency selective surface is composed of a substrate, a metal pattern layer arranged on the upper surface of the substrate, and a capacitor metal patch arranged on the lower surface, and the metal pattern layer is provided with a Jerusalem cross gap along the center;

[0012] The three-dimensional absorption structure is a periodic hollow 3D lattice array structure, the lattice unit of the three-dimensional absorption structure is square, the lattice unit includes two split ring resonators, the two split ring resonators are respectively arranged along the XOZ plane and the YOZ plane, and the split ring resonator is composed of a substrate and a conductive ink pattern layer arranged on its inner surface;

[0013] The array units of the two-dimensional frequency selective surface and the lattice units of the three-dimensional absorption structure are arranged one by one.

[0014] Furthermore, the three-dimensional absorption structure and the two-dimensional frequency selective surface are supported and fixed by foam.

[0015] Furthermore, the split ring resonator has a rectangular structure.

[0016] Based on the above technical solution, the beneficial effects of the present invention are:

[0017] In view of the problem that the design of frequency selective absorbers cannot take into account both small size and ultra-wideband absorption, the present invention adopts a hybrid design of a three-dimensional lattice array structure and a two-dimensional FSS structure, so that the designed FSR has better performance and a smaller size. In addition, the present invention uses a conductive ink impedance film to replace the traditional lumped resistor, which greatly saves costs without affecting performance. Finally, the three-dimensional frequency selective absorber with integrated penetration and absorption provided by the present invention realizes the characteristics of low-frequency wave transmission and high-frequency broadband wave absorption, while having the advantages of ultra-thinness and small unit size, good angle stability, simple structure, and easy preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the unit structure of the three-dimensional frequency selective absorber with broadband absorption characteristics in the present invention.

[0019] Figure 2 It is a schematic diagram of the structure of the three-dimensional absorption structure and the two-dimensional FSS in the present invention.

[0020] Figure 3 This is a simulation result diagram of the three-dimensional frequency selective absorber with integrated absorption and transmission in the present invention.

[0021] Figure 4 1 is the simulated reflection / transmission coefficient of the three-dimensional frequency selective absorber at various incident angles under dual polarization conditions in this embodiment, where (a) is TE polarization and (b) is TM polarization. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0023] This embodiment provides a three-dimensional frequency selective absorber with broadband absorption characteristics, which transmits waves at around 1.85 GHz, has a transmission bandwidth of about 400 MHz, and an absorption band of 5.5 to 15.5 GHz; the specific structure is as follows Figure 1 As shown, it is composed of a three-dimensional absorption structure and a two-dimensional frequency selective surface (FSS), with the XOY plane as the horizontal plane, the two-dimensional frequency selective surface is arranged along the horizontal plane, the three-dimensional absorption structure is arranged directly above the two-dimensional frequency selective surface, and an air layer is formed between the two, and the three-dimensional absorption structure and the two-dimensional frequency selective surface are supported and fixed by foam;

[0024] The two-dimensional frequency selective surface is a periodic array structure. The array unit of the two-dimensional frequency selective surface is composed of a substrate 2, a metal pattern layer 3 arranged on the upper surface of the substrate, and a capacitor metal patch 4 arranged on the lower surface. The metal pattern layer 3 is provided with a Jerusalem cross gap along the center, such as Figure 2As shown in (b), the capacitor metal patch 4 is as follows Figure 2 As shown in (c);

[0025] The three-dimensional absorption structure is a periodic hollow 3D lattice array structure. The lattice unit of the three-dimensional absorption structure is square. The lattice unit includes two split ring resonators (SRR). The two split ring resonators are respectively arranged along the XOZ plane and the YOZ plane. The split ring resonator is composed of a substrate 2 and a conductive ink pattern layer 1 arranged on its inner surface. The split ring resonator is rectangular, such as Figure 2 As shown in (a);

[0026] The array units of the two-dimensional frequency selective surface and the lattice units of the three-dimensional absorption structure are arranged one by one opposite to each other, that is, the projections of the two on the XOY plane completely overlap.

[0027] It should be noted that the present invention uses conductive ink with impedance to form a split ring resonator, which replaces the resistor to absorb the incident electromagnetic wave; the surface impedance of the conductive ink can usually be given by the following relationship: R s =1 / (σ×t), where σ represents the volume conductivity of the ink and t represents the thickness of the ink. At the same time, a two-dimensional frequency selective surface structure is used below to achieve low insertion loss wave transmission in the working frequency band.

[0028] In this embodiment, the substrate is a 0.508mm thick Rogers RO4003C dielectric substrate. In the three-dimensional absorption structure, the size of the split ring resonator is 10mm×7mm (Y axis×Z axis), the size of the conductive ink pattern is 7mm×6mm (Y axis×Z axis), the width of the opening slot is 0.3mm (Z axis), the thickness of the conductive ink pattern layer is 75um, and the volume conductivity of the conductive ink is 664. In the two-dimensional frequency selective surface (FSS), the size of the array unit is 10×10×8.508mm 3 The side length of the capacitor metal patch is 9.5mm; in the Jerusalem cross gap, the length of the central cross gap is 8.8mm and the width is 0.2mm, and the length of the surrounding gaps is 7mm and the width is 0.5mm.

[0029] CST Studio suite 2019 software was used to simulate the model structure and its size parameters. The simulation results are as follows: Figure 3As shown in the figure, it can be seen that the central passband frequency of the three-dimensional frequency selective absorber with integrated penetration and absorption is 1.84 GHz, and the insertion loss is 0.39 dB; for the absorption characteristics, S parameters can usually be used for calculation, and the absorption bandwidth range with an absorption coefficient greater than 90% is 5.49-15.5 GHz, corresponding to a relative absorption bandwidth of 95.4%; that is, the three-dimensional frequency selective absorber with integrated penetration and absorption in this embodiment can achieve wave transmission at about 1.84 GHz and wave absorption at 5.49-15.5 GHz.

[0030] like Figure 4 The figure shows the simulated reflection / transmission coefficients of the integrated three-dimensional frequency selective absorber at various incident angles under dual polarization conditions in this embodiment. It can be seen from the figure that with the increase of the incident angle, from 0° to 30°, under TE polarization, the absorption characteristics of the FSR in this embodiment are gradually reduced, and the transparent part is basically unchanged; under TM polarization, the transparent part is also unchanged, and the absorption band is gradually reduced; but under TE and TM polarizations, when the incident angle is 30°, S11 is still below -10, indicating that the FSR in this embodiment still has good absorption characteristics and has good angle stability.

[0031] In summary, the present invention provides a three-dimensional frequency selective absorber with broadband absorption characteristics, whose transparent band is below the absorbing band, has the characteristics of small size and ultra-wide band, and has good angular stability and flexible assembly characteristics, and has strong practicality.

[0032] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A three-dimensional frequency selective absorber with broadband absorption characteristics, which consists of a three-dimensional absorption structure and a two-dimensional frequency selective surface (FSS), characterized in that: Taking the XOY plane as the horizontal plane, the two-dimensional frequency selective surface is arranged along the horizontal plane, and the three-dimensional absorption structure is arranged directly above the two-dimensional frequency selective surface, and an air layer is formed between the two; The two-dimensional frequency selective surface is in a periodic array structure, and the array unit of the two-dimensional frequency selective surface is composed of a substrate, a metal pattern layer arranged on the upper surface of the substrate, and a capacitor metal patch arranged on the lower surface, and the metal pattern layer is provided with a Jerusalem cross gap along the center; The three-dimensional absorption structure is a periodic hollow 3D lattice array structure, the lattice unit of the three-dimensional absorption structure is a square in horizontal plane projection, the lattice unit includes two split ring resonators, the two split ring resonators are respectively arranged along the XOZ plane and the YOZ plane, and the split ring resonator is composed of a substrate and a conductive ink pattern layer arranged on its inner surface; The array units of the two-dimensional frequency selective surface and the lattice units of the three-dimensional absorption structure are arranged one by one.

2. The three-dimensional frequency selective absorber with broadband absorption characteristics according to claim 1, characterized in that: The three-dimensional absorption structure and the two-dimensional frequency selective surface are supported and fixed by foam.

3. The three-dimensional frequency selective absorber with broadband absorption characteristics according to claim 1, characterized in that: The split ring resonator has a rectangular structure.

Images